Linear Kinetics of Locomotion (Forces 3) Flashcards
in running, the shape of the z component of GRF depends on what?
the footfall patter of the runner (whether they have a heal-strike or a mid-foot style)
heal-strike runners have 2 peaks. what are they called?
passive peak and active peak
mid-foot runners have 1 peak, what is it called?
active peak
both running styles share this peak
explain what the ‘passive peak’ of running is (3 points)
1) rapid
2) passive - not considered to be under muscular control
3) influenced by impacted velocity, contact area, joint angles, surface stiffness, motion of body segments
explain what the ‘active peak of running is (2 points)
1) greater magnitude than passive peak
2) active - indicates the role the muscles play in force development for acceleration
explain how the Fy component changes during walking and running (2 points)
1) during locomotion, this component shows a neg phase during the first half of support as a result of backward horizontal friction between the shoe and the surface
2) this moves to positive near mid-foot stance, as force is generated by muscles pushing back against the ground
why is it difficult to measure the Fx component of walking and running ? (2 points)
1) no consistent pattern from individual to individual
2) very difficult to interpret without a video or film record of the foot contact
what relationship confirms people do slow down during the first phase of support, and speed up during the latter portion
the impulse-momentum relationship
explain 3 points of an impulse-momentum relationship curve of motion
1) area under neg portion = neg impulse
2) area under pos portion = pos impulse
3) if they equal each other then the body is moving at a constant speed
external work of walking has 2 components. what are they?
1) one caused by inertial forces as a result of speed changes in the forward direction
2) other caused by the cyclic upward displacement of the centre of gravity
the motion of the COG during walking has been modelled as an ‘inverted pendulum’. explain this using 3 points
1) when COG is behind the point of contact (heal strike), the GRF produces a neg acceleration and KE dec^ due to loss of forward speed
2) at the same time, an inc^ in the COG as the body vaults over the supporting limb. this inc^ the GPE, which reaches a max level during mid-stance
3) as the COG moves forward of the point of contact, the KE inc^ because GPE dec^ with the reduction of height in the COG
is the net change in mechanical energy during walking small or large? why?
small
the conservation of energy is not perfect, so the total energy of the COG fluctuates
does the mechanical energy fluctuate more or less during walking or running?
during running
explain, using 3 points, the differences in mechanical energy during running compared to walking
1) KE in running similar to walking, reaching min levels at mid-stance due to deceleration caused by GRF and inc^ in the latter half of support phase
2) the PE is different than in walking because it is at min at mod stance because of compliance and flexion of the support limb
3) the overall vertical exertion of the COG is less as the speed of running increases
what is there not an exchange like during running?
there is not the pendulum like exchange between KE and PE like in walking because the energies are in phase with each other during walking
